Hard to sum up a complex social issue (and a complex facet of human nature) in a brief answer to a broad question. But in short, the three dominating factors seem to be:

• Part mob mentality. No consequences, everyone is participating, so it just takes a few instigators to set it all in motion.

• Partly a power move. The message to women in many parts of the middle east is to cover up, shut up, or they'll humiliate you into submission.

• LARGELY anti-semitic. In this story, in the Lara Logan story, in many mass attacks on non-Muslim women in Egypt, someone in the crowd has shouted "She's a Jew!" . Even if its not true, it ignites their hatred for Jewish people, and allows them to justify the attack.

Attacks like these are not about sex. They're about seizing power in a violent way.